Optical MEM devices are used to modulate one or more wavelengths of light. Optical MEM devices can have applications in display, print and electrical device technologies. Examples of optical MEM devices which utilize suspended micro-ribbon structures to modulate light are disclosed in the U.S. Pat. Nos. 5,311,360, 5,841,579 and 5,808,797, all issued to Bloom et al., the contents of which are hereby incorporated by reference.
Briefly, an optical MEM device described in the above referenced patents has one or more sets of movable ribbons that comprise a support layer and a reflective top-layer. The support layer is preferably a silicon nitride layer and the reflective top-layer is preferably an aluminum layer. The ribbon structures are typically secured to a substrate through opposite ends of the ribbon, whereby center portions of the ribbons, referred to herein as the active portions, move up and down to modulate an incident light source.
Optical MEM devices described previously have relied on dielectric support layers, such as layers of silicon-nitride, with conductive and reflective top-layers, such as aluminum. Because the sides and the undersides of the ribbon are dielectric surfaces, there is a propensity for such ribbon structures to experience charging problems during operation.
Charging refers to the undesirable collection and migration of electrical charges on the insulating surfaces, or dielectric surfaces, of a MEM device. The presence of surface charging on the ribbons of an optical MEM device can perturb or shift the switching bias voltages required to operate the device causing the device to generate unreliable or irreproducible optical signals.
Currently, there is no known optical MEM device construction or method of making an optical MEM device with ribbon structures which can efficiently drain charge from the ribbon surfaces in a reliable manner. Accordingly, what is desired is an optical MEM device with reduced charging characteristics and a method for making the same.